1. Field of the Invention
The present invention relates to a combustion apparatus provided with an all primary combustion burner for supplying hot water or the like.
2. Description of the Related Art
Conventionally, there has been known a combustion apparatus for supplying hot water which is composed of an all primary combustion burner and a combustion cabinet. On the top of the combustion cabinet, there is disposed a heat exchanger; and the all primary combustion burner having a combustion plate with a plurality of burner ports is disposed inside the combustion cabinet. This kind of the combustion apparatus having the all primary combustion burner has an advantage in making the apparatus compact sized; on the contrary, however, it has a problem that heat loss is easy to occur when the combustion cabinet becomes hot.
In regard to this problem, there has been known a combustion apparatus as disclosed in, for example, Japanese Patent Laid-open No. 2007-292342, in which a ventilation gap between an outer side surface of the burner and an inner side surface of the combustion cabinet in the conventional art is maintained, and the ventilation gap is supplied with air from a fan as cooling air to form a cooling air curtain circulating on the top of the burner along the inner side surface of the combustion cabinet while the fan blows air to the burner as primary air.
According to the combustion apparatus described in the above, the combustion cabinet is cooled by the air curtain; resultantly, the heat loss of the combustion cabinet is prevented. On the other hand, however, a part of the cooling air in the ventilation gap flows into and circulates above i peripheral area of the combustion plate, and they are mixed into a mixture gas erupted from the burner ports in the peripheral area before the mixture gas is completely combusted. As a result, the air excess rate in the mixture gas becomes extremely high, which lifts up the flames from the combustion ports in the peripheral area of the combustion plate, leading to a deteriorated combustion performance.